Method of manufacturing electrical cable, and resulting product, with reduced required installation pulling force

ABSTRACT

Disclosed are cable types, including a type THHN cable, the cable types having a reduced surface coefficient of friction, and the method of manufacture thereof, in which the central conductor core and insulating layer are surrounded by a material containing nylon or thermosetting resin. A silicone based pulling lubricant for said cable, or alternatively, erucamide or stearyl erucamide for small cable gauge wire, is incorporated, by alternate methods, with the resin material from which the outer sheath is extruded, and is effective to reduce the required pulling force between the formed cable and a conduit during installation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/590,881, filed May 9, 2017, which is a continuation of U.S.application Ser. No. 14/858,872, filed Sep. 18, 2015, which is acontinuation of U.S. application Ser. No. 14/144,150, filed Dec. 30,2013, now issued as U.S. Pat. No. 9,142,336 on Sep. 22, 2015, which is acontinuation of U.S. application Ser. No. 13/774,677, filed Feb. 22,2013, now U.S. Pat. No. 8,616,918, issued Dec. 31, 2013, which is acontinuation of U.S. application Ser. No. 13/274,052, filed Oct. 14,2011, now U.S. Pat. No. 8,382,518, issued Feb. 26, 2013, which is acontinuation of U.S. application Ser. No. 12/787,877, filed May 26,2010, now U.S. Pat. No. 8,043,119, issued Oct. 25, 2011, which is acontinuation of U.S. application Ser. No. 11/675,441, filed Feb. 15,2007, now U.S. Pat. No. 7,749,024, issued Jul. 6, 2010, which is acontinuation-in-part of U.S. application Ser. No. 11/120,487, filed May3, 2005, now abandoned, which is a continuation-in-part of U.S.application Ser. No. 10/952,294, filed Sep. 28, 2004, now U.S. Pat. No.7,411,129, issued Aug. 12, 2008. Each patent and patent applicationidentified above is incorporated here by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to electrical cables, more particularly toTHHN electrical cables, and even more particularly to methods forreducing the surface coefficient of friction and required installationpulling force thereof, as well as preferred pulling lubricantcompositions for effecting such reductions.

BACKGROUND OF THE INVENTION

Electrical cables include a conductor core and typically include anouter jacket or sheath. The term “sheath,” as used herein and throughoutthe specification and claims, is defined to mean the outermostprotective jacket or covering surrounding a conductor core, whether of asingle type material or multiple layers of the same or differentmaterial. The conductor core may typically be, for example, a singlemetal wire, multiple small wires twisted together to make a “stranded”cable, or multiple insulated wires or other type electrical conductorsacting together to serve a particular function (e.g., three-phaseconnection). The sheath may comprise one or more layers of polymeric orother material to provide physical, mechanical, electrical insulatingand/or chemical protection for the underlying cable components. For thepurpose of type THHN cable of the present invention, the exteriorportion of the sheath is of nylon. Specifically, type THHN cablecomprises a conductor core of a single solid or stranded conductor,surrounded by a layer of polyvinyl chloride (PVC) electrical insulation,covered by an outer layer of nylon.

Installation of electrical cable often requires that it be pulledthrough tight spaces or small openings in, and in engagement with,narrow conduits, raceways, cabletrays, or passageways in rafters orjoists. This becomes problematic since the exterior surface of the cablesheath normally has a high coefficient of friction, therefore requiringa large pulling force. Moreover, installation parameters include maximumallowable cable pulling tension and/or sidewall pressure limits.Exceeding these limits can result in degradation of the cable, physicaldamage and inferior installation.

To overcome this problem, the general industry practice has been to coatthe exterior surface of the cable sheath with a pulling lubricant at thejob site in order to reduce the coefficient of friction between thissurface and the conduit walls or like surfaces, typically usingvaselines or lubricants produced specifically, and well known in theindustry for such purpose, such as Yellow 77® (hereinafter, “Y 77”). Theterm “pulling lubricant,” as used herein and throughout thespecification and claims, is defined to mean lubricating material whichsufficiently reduces the coefficient of friction of the exterior surfaceof the sheath of the cable to facilitate the pulling of the cable.

The aforementioned industry practice of applying a pulling lubricantlike Y 77 to the finished cable at the job site poses problems,principally due to the additional time, expense and manpower required tolubricate the finished cable surface at the job site as well as to cleanup after the lubricating process is completed. Alternative solutionshave been tried but are generally unsuccessful, including the extrusionof a lubricant layer over the extruded polymeric sheath during themanufacturing of the cable, or the application of granules of materialto the still-hot sheath during the extrusion process, which granules aredesigned to become detached when the cable is pulled through the duct.However, these solutions not only require major alterations of themanufacturing line, but result in a loss in manufacturing time,increased economic costs, and undesirable fluctuations in thegeometrical dimensions of the cable sheaths.

It is also important to an understanding of the present invention toknow the difference between what are referred to as “pulling lubricants”and what are “processing lubricants.” A pulling lubricant is a lubricantthat appears at the outside surface of the sheath of the cable and iseffective to lower the surface coefficient of friction such as to reducethe force necessary to pull the cable along or through building surfacesor enclosures. A processing lubricant is lubricating material that isused to facilitate the cable manufacturing process, such as the flow ofpolymer chains during any polymer compounding as well as during theextrusion processes while the polymer is in its molten or melt phase.Cable manufacturers have long used processing lubricants, such asstearic acid or ethylene bis-stearamide wax, as a minor component of thepolymeric compound from which the cable sheath is formed. Because aprocessing lubricant is normally not effective except when the polymeris in this melt phase, the effect of a processing lubricant isessentially non-existent in the final hardened polymer sheath of thecable. Even where there may be an excessive amount of the processinglubricant, a separate pulling lubricant would still be required tosufficiently reduce the cable sheaths' exterior surface coefficient offriction in order to minimize the pulling force necessary to install thecable.

Accordingly, there has been a long-felt need for an effective method ofproviding a pulling lubricant at the exterior surface of the finishedcable, and particularly the finished THHN cable, which is effective toreduce the cable surface coefficient of friction and minimize therequired installation pulling force, without incurring the inconvenienceand time-consuming operation and expense associated with the applicationof the pulling lubricant at the installation site, nor significantlyincreasing the complexity and cost of the manufacturing process, norundesirably altering the geometrical characteristics of the cablesheaths.

SUMMARY OF THE INVENTION

The process of the present invention accomplishes these objectives forTHHN cable by a cable manufacturing process in which a particularpulling lubricant, of optimum weight percentage or quantity, isintroduced into the manufacturing process at a particular stage ofmanufacture, which results in the pulling lubricant being present in theouter sheath, so that it is available to reduce the coefficient offriction of the exterior sheath surface when the cable is to beinstalled. Depending upon the material of the sheath and the type oflubricant, this may be as a consequence of the migration, or delayedmigration or “blooming,” of the pulling lubricant to the sheath surface;or alternatively, due to the permeation of the pulling lubricantthroughout the sheath. Under these circumstances, the pulling lubricantis effective to lower the surface coefficient of friction below that ofthe inherent coefficient of friction of the material from which theouter layer of the THHN sheath is formed, thereby reducing the requiredinstallation pulling force.

In accordance with the process of the invention, and as described belowin greater detail, the pulling lubricant is selectively chosen toprovide the optimum results with respect to the particular nylon sheathmaterial, and may alternately be introduced into the THHN cablemanufacturing process at various stages, ranging from the initialcompounding of the lubricant with the polymeric nylon material to formlubricated pellets from which the sheath is to be formed, to mixing thelubricant with the nylon sheath material before introduction of themixture into the extrusion process, to its introduction into the sheathextrusion process while the nylon sheath forming material is in itsmolten state.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other details and aspects of the invention, as well as theadvantages thereof, will be more readily understood and appreciated bythose skilled in the art from the following detailed description, takenin conjunction with the accompanying drawings, in which:

FIG. 1 is a diagrammatic representation of typical equipment used in themanufacture of cable in accordance with the present invention, whenmixing the lubricant with the nylon material prior to extrusion;

FIG. 2 is a graphical representation of test data comparing the effectof different pulling lubricants in small size THHN cable in which theouter sheath material is nylon;

FIG. 3 is a graphical representation of test data comparing both theeffects of different pulling lubricants and different percentages ofpulling lubricant in large size THHN cable in which the outer sheathmaterial is nylon;

FIGS. 4 and 5 are representations of test devices which may be used tocreate the aforementioned test data; and

FIG. 6 is a section view of a THHN cable produced in accordance with theprocess of the present invention.

DESCRIPTION

Referring initially to FIG. 1, there is depicted typical equipment 11for manufacturing electrical cable 12 in accordance with one process ofthe present invention. The outer sheath of the cable is of an extrudedpolymer material, specifically nylon. The equipment 11 may include areel 13 which supplies conductor wire 14 to an extruding head 15. Inflow communication with the extrusion head is a tank 16 of the nylonpellets 17. A tank 18 with the desired pulling lubricant 19 is adaptedto be in flow communication with the tank 16 by way of conduit 22, thusenabling the mixing of the pulling lubricant with the nylon pellets 17,the mixture thereafter introduced into the extruder. Alternatively, thetank may be adapted to be in fluid communication with the extruder orextrusion head 15, by way of conduit 23, downstream from the point ofentry of the nylon material, thus allowing the pulling lubricant to mixwith the nylon material while in its molten state in the extruder orextruder head. A cooling box 20 for cooling the extruded product isprovided, and a reel 21 is positioned for taking up the resulting cableassembly 12. When the final cable construction is such that there aremultiple layers of sheath material, the pulling lubricant shoulddesirably be incorporated into the outermost layer.

As is therefore evident, the pulling lubricant can be mixed with thematerial from which the outer sheath is to be extruded prior toextrusion or, alternatively, introduced into the extruding head forsubsequent mixing with the molten extrusion material as the sheath isbeing formed. As a further alternative, the pulling lubricant can beinitially compounded with the polymeric material of the pelletsthemselves in a process upstream of that depicted in FIG. 1, therebyforming lubricated polymeric pellets, thus eliminating the need for tank18 and conduits 22 and 23.

Polymeric materials that can be used for an insulating layer or outersheath of different type of cable include polyethylene, polypropylene,polyvinylchloride, organic polymeric thermosetting and thermoplasticresins and elastomers, polyolefins, copolymers, vinyls, olefin-vinylcopolymers, polyamides, acrylics, polyesters, fluorocarbons, and thelike. As previously described, for the THHN cable of the presentinvention, the conductor core of a single solid or stranded conductor issurrounded by an insulating layer of PVC covered by an outer sheath of apolyamide (e.g., nylon).

In accordance with the testing subsequently described, it has beendetermined that, for THHN cable, silicone oil is the preferred pullinglubricant. For small gauge THHN wire, erucamide is an alternativepreferred pulling lubricant, to be incorporated in the nylon sheath.

The efficacy of these pulling lubricants for the nylon sheath, andspecifically an optimum range for the quantity of such lubricants, inaccordance with the invention, has been proven by the use of varioustests. Prior to discussing the results of such tests, these test methodsand their equipment are described as follows:

Testing Methods

Coefficient of Friction Test

Referring now to FIG. 4, diagrammatically illustrated is the apparatusfor a coefficient of friction test. The coefficient of friction testapparatus was developed to give a consistent way to determine the inputvalues necessary to use the industry-standard program published byPolyWater Corporation to calculate a real-world coefficient of frictionfor a given cable being pulled in conduit. Given the inputs for theconduit setup, the back tension on the wire, and the pulling tension onthe pulling rope, this program back-calculated a coefficient of frictionfor the cable by subtracting the back tension from the pulling tensionand attributing the remaining tension on the rope to frictional forcesbetween the cable and the conduit.

The overall setup used a pulling rope threaded through ˜40′ of PVCconduit (appropriately sized for the cable being pulled) with two 90°bends. Three 100′ pieces of THHN cable were cut and laid out parallel toone another in line with the first straight section of conduit, and therope connected to them using industry-standard practice. The other endof the THHN cable was attached to a metal cable which was wrapped arounda cylinder with an air brake to allow the application of constant backtension on the setup.

The metal cable was threaded through a load cell so that it could bemonitored in real-time, and continuously logged. The pulling rope wassimilarly threaded through a load cell and constantly monitored andlogged. Values for both back tension and pulling tension were logged forthe time it took to pull cable through the conduit run. These valueswere then averaged and used in the PolyWater program to calculatecoefficient of friction.

Specific Type THHN Tests

Initial tests of small gauge Type THHN wire were performed using thesmall-scale tension tester shown in FIG. 5. In this test, multipleindividual American Wire Gauge (AWG) size 12 THHN wires were provided onthe payoff and attached to a metal pulling tape that was threadedthrough an arrangement of ½″ conduit that included about 50 feet ofstraight conduit and four 90° bends. A pulling rope was attached to theother end of the pulling tape and a tugger was used to pull the cablearrangement through the conduit. The rope was threaded through a pulleyarrangement that used a load cell to monitor rope tension while the wirewas pulled through the conduit. This tension was continuously logged andaveraged to give an average pulling force for the pull. This forcecorrelated directly to the coefficient of friction for the cable.

Using the data obtained from the small scale pull test of FIG. 5, FIG. 2illustrates a comparison of the different required pulling forces for asmall gauge cable consisting of multiple (AWG) size 12 THHN conductors.The test subjects had 0.25-0.85% of two different potential pullinglubricants, erucamide and stearyl erucamide, mixed into the outer nylonsheath. Results of the test are shown in FIG. 2 and compared to theresults for the standard THHN product without any pulling lubricant andwith the externally applied industry-standard Y77. This test shows thaterucamide is one preferred lubricant for small gauge THHN cable, in anoptimum percentage of approximately 0.85%, by weight.

Next, large gauge Type THHN cable was tested. Using the coefficient offriction test of FIG. 4, FIG. 3 illustrates the different values ofsurface coefficient of friction of the exterior surface of the sheath,for cables consisting of three individual large gauge AWG 4/0 THHNconductors, for varying percentages of the pulling lubricant, siliconeoil, of varying molecular weights. The two lubricants compared in FIG. 3are a high-molecular weight silicone oil (HMW Si) and a lower molecularweight silicone oil (LMW Si). Comparison results are shown for this sameTHHN cable arrangement lubricated with industry-standard Y77, as well aswith respect to three other trial pulling lubricants, fluorinated oil,molydisulfide, and stearyl erucamide. The results in FIG. 3 illustratethat, while other pulling lubricants can reduce the coefficient offriction of the exterior surface of the cable, the preferred pullinglubricant for THHN cable, and particularly large gauge THHN cable, is ahigh molecular weight silicone oil added at a level of approximately 9%,by weight, or higher.

In accordance with an advantage of the present invention, the pullinglubricant that is incorporated in the sheath is present at the outersurface of the sheath when the cable engages, or in response to thecable's engagement with, the duct or other structure through which thecable is to be pulled. For the THHN cable of the present invention,where the outer sheath is of nylon and the preferred pulling lubricantis high molecular weight silicone oil, this silicon-based lubricantpermeates the entire nylon sheath portion and is, in effect,continuously squeezed to the sheath surface in what is referred to asthe “sponge effect,” when the cable is pulled through the duct.

Compounding with Pulling Lubricant

As previously described, the pulling lubricant may be incorporated intothe extruded sheath (or the outer layer of the cable sheath if thesheath is of multiple layers) by initially compounding the lubricantwith the (outer) sheath material to be extruded. To prepare thelubricated blend of the present invention, the resin and additionalcomponents, including the pulling lubricant, are fed into any one of anumber of commonly used compounding machines, such as a twin-screwcompounding extruder, Buss kneader, Banbury mixer, two-roll mill, orother heated shear-type mixer. The melted, homogeneous blend is thenextruded into strands or cut into strips that may be subsequentlychopped into easily handled pellets. The so-prepared lubricated pelletsare then fed into the extruder for forming the outer sheath.

THHN Cable

THHN and THWN-2 are types of insulated electrical conductors that covera broad range of wire sizes and applications. THHN or THWN-2 conductorsare typically 600 volt copper conductors with a sheath comprising anouter layer of nylon surrounding a layer of thermoplastic insulation andare heat, moisture, oil, and gasoline resistant. THHN cable is primarilyused in conduit and cable trays for services, feeders, and branchcircuits in commercial or industrial applications as specified in theNational Electrical Code and is suitable for use in dry locations attemperatures not to exceed 90° C. Type THWN-2 cable is suitable for usein wet or dry locations at temperatures not to exceed 90° C. or not toexceed 75° C. when exposed to oil or coolant. Type THHN or THWN-2conductors are usually annealed (soft) copper, insulated with a tough,heat and moisture resistant polyvinylchloride (PVC), over which apolyamide layer, specifically nylon, is applied. Many cables, includingthose addressed by the present invention, can be “multi-rated,”simultaneously qualifying for rating as THHN or THWN-2.

Referring now to FIG. 6, there is illustrated a THHN cable 24constructed in accordance with the process of the invention. The cableis characterized by a sheath comprising an extruded layer 25 of PVCinsulation material and an overlying extruded thin layer 26 of nylon,the sheath surrounding a central electric conductor 27 which is usually,though not exclusively, of copper. The only limitation on the type ofpulling lubricant to be incorporated into the extruded outer nylonsheath is that it be sufficiently compatible with nylon to beco-processed with it, and particularly when compounded with nylon, thatit be robust enough to withstand the high processing temperature fornylon, which is typically about 500° F. However, it has been found thatfor THHN cable, this lubricant is preferably a high molecular weight,high viscosity silicone fluid; for small gauge THHN wire, as analternative, erucamide or stearyl erucamide.

Two industry-standard processes can be used to produce this product, theso called co-extrusion method and the tandem extrusion method. In bothprocesses, the conductor, either solid or stranded, is first introducedinto the extrusion head where the heated, melted PVC insulation compoundis introduced and applied to the circumference of the conductor. In theco-extrusion process, the melted nylon compound is introduced into thesame extrusion head and applied together with the PVC to the conductor,in a two-layer orientation. In the tandem process the PVC-coatedconductor leaves the first extrusion head and is introduced into asecond, separate extrusion head where the melted nylon is applied to thesurface. In both cases, the final product is then introduced into acooling water bath and ultimately the cooled product is wound ontoreels. In either case, the nylon material is preferably initiallycompounded with the pulling lubricant to provide the so-lubricatedextrusion pellets.

As shown in FIG. 2, small gauge THHN cable prepared, as described, withnylon as the outer layer of the sheath, and containing 0.25%, 0.50% and0.85%, by weight, of stearyl erucamide, had an average pulling force of18.1 lbs, 16 lbs and 18.5 lbs, respectively. Even better, small gaugeTHHN cable containing 0.25%, 0.50% and 0.85%, by weight, of erucamidehad an average pulling force of 13.2 lbs, 10.3 lbs and 9.6 lbs,respectively. Comparably, the pulling force for a THHN cable with nopulling lubricant was measured at 38.5 lbs, and THHN cable with only Y77 applied to the exterior surface was measured at 15.3 lbs. FIG. 3, onthe other hand, illustrates the results when silicone oil is used inTHHN cable, compared to other potential lubricants, illustratingsilicone oil as a much preferred pulling lubricant for this type cable.

Although the aforementioned description references specific embodimentsand processing techniques of the invention, it is to be understood thatthese are only illustrative. For example, although the description hasbeen with respect to electrical cable, it is also applicable to othertypes of non-electrical cable such as, for example, fiber optic cable.Additional modifications may be made to the described embodiments andtechniques without departing from the spirit and the scope of theinvention as defined solely by the appended claims.

1-19) (canceled) 20) A thermoplastic high heat-resistant nylon-coated(THHN) electrical cable having a reduced installation pulling forcethrough a building passageway defined by a PVC conduit setup sized toaccomodate the THHN electrical cable and having at least two 90° bendswithin the PVC conduit setup, the THHN electrical cable comprising: atleast one conductor capable of carrying an electrical current throughthe THHN electrical cable, wherein the conductor is formed at least inpart from a metal; and, a sheath for protecting the conductor, whereinthe sheath comprises: an insulating layer surrounding the conductor andproviding electrical insulation to the conductor, wherein the insulatinglayer is formed at least in part from extruded polyvinyl chloride (PVC);and an outer layer surrounding, contacting, and forming a coating forthe insulating layer, wherein the outer layer comprises a solidifiedextrusion of a material mixture, the material mixture comprising: anylon material; and a pulling lubricant mixed within at least a portionof the nylon material, wherein at least a portion of the pullinglubricant is present at an exterior surface of the sheath to reduce theamount of force required to pull the cable through the buildingpassageway; and wherein the outer layer is both resistant to heat,moisture, oil, and gasoline and provides the THHN electrical cable withthe physical characteristic of requiring at least about 30% less forceto pull the electrical cable through the building passageway compared toan amount of force required to pull a non-lubricated THHN electricalcable having an extruded sheath without the pulling lubricant mixedtherein through the building passageway. 21) The thermoplastic highheat-resistant nylon-coated (THHN) electrical cable of claim 20, whereinthe pulling lubricant comprises a silicone oil. 22) The thermoplastichigh heat-resistant nylon-coated (THHN) electrical cable of claim 20,wherein the pulling lubricant comprises a high molecular weight siliconebased pulling lubricant. 23) The thermoplastic high heat-resistantnylon-coated (THHN) electrical cable of claim 20, wherein the pullinglubricant comprises a low molecular weight silicone based pullinglubricant. 24) The thermoplastic high heat-resistant nylon-coated (THHN)electrical cable of claim 20, wherein the pulling lubricant compriseserucamide. 25) The thermoplastic high heat-resistant nylon-coated (THHN)electrical cable of claim 20, wherein the at least one conductorcomprises a plurality of grouped conductors. 26) The thermoplastic highheat-resistant nylon-coated (THHN) electrical cable of claim 20, whereinthe at least one conductor is a large gauge conductor. 27) Thethermoplastic high heat-resistant nylon-coated (THHN) electrical cableof claim 26, wherein the at least one conductor comprises an AWG 4/0conductor. 28) The thermoplastic high heat-resistant nylon-coated (THHN)electrical cable of claim 20, wherein the sheath is formed withgeometrical characteristics that are not altered relative to thegeometrical characteristics of the extruded sheath of the non-lubricatedTHHN cable. 29) The thermoplastic high heat-resistant nylon-coated(THHN) electrical cable of claim 28, wherein the sheath has a roundprofile. 30) The thermoplastic high heat-resistant nylon-coated (THHN)electrical cable of claim 20, wherein the THHN electrical cable is ratedfor use in dry locations at temperatures not to exceed 90° C. 31) Thethermoplastic high heat-resistant nylon-coated (THHN) electrical cableof claim 20, wherein the THHN electrical cable is rated to carry currentat voltages not to exceed 600 Volts. 32) A thermoplastic highheat-resistant nylon-coated (THHN) electrical cable having a reducedinstallation pulling force through a building passageway defined by aPVC conduit setup sized to accomodate the THHN electrical cable andhaving at least two 90° bends within the PVC conduit setup, the THHNelectrical cable comprising: at least one conductor capable of carryingan electrical current through the THHN electrical cable, wherein theconductor is formed at least in part from a metal; and, a sheath forprotecting the conductor, wherein the sheath comprises: an insulatinglayer surrounding the conductor and providing electrical insulation tothe conductor, wherein the insulating layer is formed at least in partfrom extruded polyvinyl chloride (PVC); and an outer layer surrounding,contacting, and forming a coating for the insulating layer, wherein theouter layer comprises a solidified extrusion of a material mixture, thematerial mixture comprising: a nylon material; and a pulling lubricantmixed within at least a portion of the nylon material, wherein at leasta portion of the pulling lubricant is present at an exterior surface ofthe sheath to reduce the amount of force required to pull the cablethrough the building passageway; and wherein the outer layer is bothresistant to heat, moisture, oil, and gasoline and provides the THHNelectrical cable with the physical characteristic of requiring at leastabout 50% less force to pull the electrical cable through the buildingpassageway compared to an amount of force required to pull anon-lubricated THHN electrical cable having an extruded sheath withoutthe pulling lubricant mixed therein through the building passageway. 33)The thermoplastic high heat-resistant nylon-coated (THHN) electricalcable of claim 32, wherein the sheath is formed with geometricalcharacteristics that are not altered relative to the geometricalcharacteristics of the extruded sheath of the non-lubricated THHN cable.34) The thermoplastic high heat-resistant nylon-coated (THHN) electricalcable of claim 33, wherein the sheath has a round profile. 35) Anon-metallic sheathed (NM-B) electrical cable having a reducedinstallation pulling force through a building passageway extendingthrough throughholes drilled at a 15 degree angle through a broadface ofeach of four 2″×4″ wood blocks, wherein the wood blocks are lineaerlyspaced apart from one another and are offset such that a centerline ofeach of the throughholes is offset by 10″ relative to one another, theNM-B electrical cable comprising: a conductor core comprising at leasttwo insulated metal conductors capable of carrying an electrical currentthrough the NM-B electrical cable, wherein the conductor is formed atleast in part from metal; and a sheath for protecting the conductorcore, wherein the sheath comprises a solidified extrusion of a materialmixture, the material mixture comprising: an insulating materialproviding electrical insulation to the conductor core, wherein theinsulating material comprises polyvinyl chloride; and a pullinglubricant mixed with at least a portion of the insulating material,wherein at least a portion of the pulling lubricant is present at anexterior surface of the sheath to reduce the amount of force required topull the cable through the building passageway; and wherein the sheathprovides the NM-B electrical cable with the physical characteristic ofrequiring at least about 30% less force to pull the electrical cablethrough the building passageway compared to an amount of force requiredto pull a non-lubricated NM-B electrical cable having an extruded PVCjacket without the pulling lubricant mixed therein through the buildingpassageway. 36) The NM-B electrical cable of claim 35, wherein thepulling lubricant comprises one of erucamide or oleamide. 37) The NM-Belectrical cable of claim 36, wherein the pulling lubricant comprises asilicone pulling lubricant. 38) The NM-B electrical cable of claim 36,wherein each of the at least two metal conductors are 14-gauge metalconductors. 39) The NM-B electrical cable of claim 36, wherein each ofthe at least two metal conductors are 12-gauge metal conductors.